<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app">
      <p v-bind:class="cls1"></p>
      <p :class="cls1" class="abc"></p>
      <p :class="cls1" :class="cls2">123</p>
      <p :class="cls3">123</p>
      <p :class="{b: isB, c: isC}"></p>
      <p :class="['a', {'b': isB}]">123</p>
  </div>
</body>
<script src="./lib/vue.js"></script>
<script>
  new Vue({
    el: "#app",
    data: {
      cls1: "a",
      cls2: "b",
      cls3: "a b c",
      isB: true,
      isC: true
    }
  })
</script>
</html>